Apple has released the latest iPhone operating system upgrade, called iOS4, which offers multitasking and more.

Multitasking is, of course, the most long-awaited of new features, but they will be available only to owners of the iPhone 3GS, 4 and new-generation iPod Touch. Owners of the 3G model and iPod Touches sold in 2008 will get some of the new features (but not multitasking), but processing power limits the scale of further upgrades. If you have an original (2007-8 ) iPhone or iPod Touch, then sorry - it's not going to happen.

Multitasking: With a double-click of the home button, you'll be taken to a screen showing all running applications. This enables background audio – a big win for those who like listening to the radio on the move but don't like being locked in to one application. Multitasking is expected to bring a boost for Skype, as new VOIP (voice over IP) technology enables calls to be made while the application is closed. (Charles Arthur adds: arguably, this is cooperative "multitasking" like in the classic MacOS days: the foremost app gets pretty much everything.)

Folders: Drag your apps into a named folder and save it on your dock or, alternatively, clump all the useless (read: default) ones into a folder and drop it on your last homepage.

Enhanced mail: For too long mail has been clunky to use – now you can have a merged the viewing of multiple inboxes, open attachments in a third-party app, and your emails will be threaded. However, there's still no "Mark all as read" button – leaving some time-constrained Twitter users fuming.

iBooks: Read and purchase ebooks direct from your handset with this app launched alongside the iPad.

5x camera zoom: Zoom comes free with the iPhone 4's 5-megapixel camera, but now those with a 3GS (3.2-megapixel) camera can also get a close up. Those with older models will have to move towards the photo subject.

Enhanced video: This is cool. Tapping the screen whilst shooting video will focus the recording on a chosen subject. Simple and smart. Great for those with iPhone 4 HD recording.

Other iOS4 features:

Spell check. You'll still have autocomplete (to turn 'new hand on deck' to 'new Han on deck') but now there's no excuses for misspelt emails.